Automatic conveyers are used extensively in industry, commercially, and in service operations such as the post office. The conveyers may be hundreds and even thousands of feet in length and carry their loads to various work stations, storage areas, etc. The conveyer system of the post-office type, used herein for explanation, has a primary or trunk line conveyer and secondary or shunt line conveyers branching off the primary conveyer. The primary conveyer usually leads from the point of reception of the bulk loads, past the work, processing and storage stations, to the point of exit of processed loads for shipment out of the installation. The primary conveyer usually runs continuously and thus the loads on it travel continuously. To work, process and/or store the loads, the loads must be shunted to the secondary conveyers where they can be handled without interference with the flow on the primary conveyer. Thus the secondary conveyers lead at an angle from the primary conveyer and the loads are shunted off the primary conveyer by a shunting device onto the secondary conveyer and again shunted back onto the primary conveyer by a shunting device after handling.
The shunting devices are usually electro-mechanical servomechanisms and various controls, air cylinders, signals, switches, solenoids, etc. are employed to activate the shunting devices at the right time for the right load moving onto or off the secondary conveyers. The automatic control system may be any suitable type to accomplish the desired end results.
The loads are usually heavy and more often very heavy and, since the conveyer drive is powerful, the impact of the loads on the shunting devices are very forceful and require very strong shunting devices to overcome the forces involved so that the loads are properly and reliably shunted and without the shunting devices breaking down or wearing out at an early time.
The usual prior art shunting device employs a very large and powerful solenoid or air cylinder to position, and, more importantly, to hold the shunting bar against the forces involved in diverting a heavy load traveling at a rapid rate from one to another conveyer. The weight and speed together with the change of direction builds up considerable momentum and inertia. The force of the diversion in shunting is thus borne entirely by the solenoids or air cylinders in the prior art devices. While mechanical advantage of various linkage is employed, it is usually insufficient as the action must be relatively quick and the advance to and retraction from the shunting position is by the same linkage. Thus the solenoids or air cylinders cannot be protected entirely by linkage and the strain on the solenoids or air cylinders cause them to wear out much faster than the rest of the automatic control system. This results in breakdown at the shunting stations and general havoc in the handling of the loads with jams, spills, breakage, and scattering resulting. It takes some time to replace a big solenoid or air cylinder and big solenoids and air cylinders are expensive. They also require more current and voltage or air pressure supply to operate than the other controls in the system, and thus supplemental wiring and lines is required. Moreover, the big solenoids or air cylinders cannot be replaced by the other low-voltage solenoids or small cylinders in the system so that a stock of big solenoids or air cylinders must be kept on hand or the station abandoned until one is obtained. The condition that the solenoid or air cylinder must resist the momentum and inertia of the force of the impact and of the shift of the load causes most of the trouble as the tug-of-war between the load and the energized solenoid or pressurized air cylinder tries to pull the armature out of the solenoid or the piston out of the cylinder while the EMF or air pressure tries to hold it in.